1. Field of the Invention
The present invention relates to fluid filled mattresses and more specifically to a gusset panel construction having square corners.
2. Discussion of the Prior Art
Typically, bed frames consist of a headboard, a footboard, and sideboards which define a generally rectangular chamber for receipt of a mattress. With this type of frame construction, it is particularly desirable to provide a mattress having the generally rectangular configuration of the chamber formed by the bed frame. Such a mattress would have generally square corners, with radii not exceeding three inches, which could substantially fill the rectangular chamber of the bed frame.
Perhaps the mattress characteristic of greatest concern, however, is that which maximizes the integrity of the fluid cavity. This is particularly important if the mattress is to be filled with a liquid. Under such conditions, a leak in the fluid cavity could permit escape of the liquid with consequent flooding resulting in damage to the bed frame and the adjacent room.
In a mattress construction of the prior art, a generally rectangular configuration is provided as disclosed by C. Mollura in U.S. Pat. No. 3,825,172 for Tubular Flexible Bag With Lap Welded Ends.
In this construction, a very large, single sheet of heat sealable vinyl is formed into the shape of a tube to provide the top, bottom, and two longitudinal sides of the mattress. Two end panels are provided and heat sealed to the ends of this tube. A specially formed die is provided with a cross-section having substantially the shape desired for the end of the mattress. At each end of the tube the marginal edges are folded over this die and one of the end panels is heat sealed to these marginal edges.
Although this mattress construction has a generally rectangular configuration, it has been most difficult to construct due to the very large size of the sheet forming the tube. In addition, the entire heat seal forming the four corners at each end of the mattress, has necessarily been formed in a single step. As a consequence, it has been very difficult to control the flow of material in this heat sealing step, and the fluid integrity of the mattress has suffered considerably resulting in many "leakers".
A preferred type of construction has been the gusset panel construction. In this type of mattress, upper and lower sheets have been provided to form the top and the bottom of the mattress. A gusset panel forming the sides and ends of the mattress has been connected between the peripheral edges of the top and bottom sheet. Such a construction is disclosed by Penn et al in U.S. Pat. No. 3,778,852.
This type of construction is much easier to manufacture but it has been particularly difficult to provide the mattress with square corners. As a consequence, the corners have been rounded to a radius such as 8 inches. To accommodate this configuration within the conventionally rectangular bed frame, it has been necessary to provide corner filling sections having large radii of curvature in order to support the rounded corners of the mattress.
Square corners in this gusset type mattress construction have been difficult to form since a large portion of the vinyl material has tended to gather at the corner when the heat seal is made. This excess of material creates an excess of vinyl flow which has tended to weaken the integrity of the mattress at the corners.